This invention relates to a device and method for resharpening the cutting edge of saws used for cutting wafers from bar-shaped or block-shaped workpieces, particularly semiconductor material. More specifically, it relates to such a device and process wherein the cutting edge of the saw may be resharpened while the tool is cutting.
In the centerhole sawing of bars, especially those made of semiconductor material (i.e., silicon, germanium arsenide, indium phosphide or oxidic material such as quartz, ruby, spinel or garnet, e.g., gallium gadolinium garnet), a highly geometric quality is demanded. This especially applies to silicon wafers having diameters of at least about 10 cm which are used as the basic material for the manufacture of high integrated electronic components. The constant increase in the packing density of such components is accompanied by distinctly closer tolerances with regard to the wafer geometry, which is essentially determined by the precision during the cutting operation.
The geometric quality of wafers, sawn from bars or blocks, the thickness of which is generally in the range of about 100 to 1,000 .mu.m, can be evaluated, e.g., by a parameter known as "warp". This is the difference between the maximum and minimum distance of the center wafer surface from a reference plane. The warp of a wafer can be established according to ASTM Standard F 657-80.
It is known from EP-A-196,642 that the warp in the wafers obtained is effected by the cutting edge of the cutting tool which removes the material. In general, a centerhole saw blade or outer cutting saw blade, if resharpened during the sawing operation upon deviation from the normal progress of the art, will yield more precise cuts (i.e., it will improve the warp of the wafers). During this process, it is not the entire cutting edge which is reground but primarily the cutting-edge lateral surface which is nearer the nominal cutting line.
In this publication, a device is disclosed for performing the resharpening operation. During the sawing process, the cutting edge passes through a recess in a workhead. Inside the workhead is a band, adjustable in its inclination and covered with abrasive grains, which can be guided to the cutting edge lateral surface via a roller system, when required. However, this device is complicated and susceptible to breakdown.